1. Field of the Invention
The present invention relates in general to portable spreading devices. More particularly, the invention relates to hand-held, manually operated spreading devices for use in broadcasting particulate materials such as granular fertilizers and the like.
2. Description of Related Art
Various portable, hand-held material spreading or broadcasting devices have been disclosed heretofore. For example, U.S. Pat. Nos. 3,157,402; 3,226,461 and 4,492,341 show versions of such devices which employ valve members normally spring biased to a closed position for shutting off flow of material from a storage chamber to a broadcasting impeller. In the devices disclosed therein, the valve member is opened by operation of a manually displaceable actuating member to enable material to flow from the storage chamber onto the broadcasting impeller. The actuating member is positioned for engagement and displacement by a finger, usually a thumb, of the hand grasping the handle. A crank handle is provided for manipulation by the user's other hand to cause the impeller to rotate and broadcast the material deposited thereon. The devices also include adjustment members which may be set to determine the degree of opening of the valve member from fully open to some intermediate position upon operation of the actuating member.
These prior devices have been found to present problems in regard to their tendency to break as a result of the user subjecting the operating components of the devices to overstressed conditions by exerting an excess force on the actuating member in an attempt to achieve a greater flow of material through the device. For example, U.S. Pat. No. 4,492,341 attempts to provide a solution to this problem by installing a stop element adjacent the actuating member in order to prevent excessive displacement of the actuating member. Also, the actuating member supporting structure is formed from a material and is dimensioned to flex without breaking upon forced movement of the actuating member. However, these proposed modifications have not fully solved the inherent premature destruction problems encountered with these prior devices. Furthermore, these modifications have not totally corrected another problem in the design of these prior devices. That is, if sufficient force is applied on the actuating member by a user of the device, the actuating member may be displaced from its original set position to an unselected position whereby the valve opening is reset to provide an undesired material flow rate from the device.
In addition, as designed these prior devices normally require constant finger or thumb pressure to be applied to the actuating member in order to continue dispensing particulate material for broadcast spreading. Accordingly, a human engineering or ergonomic problem is presented since these prior devices have not been configured to satisfactorily accommodate prolonged finger or thumb engagement with the actuating member. In practice, it has been found that the finger or thumb which is employed to hold the actuating member in operative engagement encounters an undesirably high degree of fatigue as a result of the application of constant pressure.
Furthermore, it has been found that as the user's finger or thumb tires through prolonged usage of these prior devices, the finger or thumb will back off in exerting force on the actuating member and the extent of valve opening will be impacted thereby resulting in varying levels of granular material being dispensed or applied to adjoining sections of a lawn or other such area causing striated or patchy growth therein. Also, in the construction of these devices, there is no capability to release the thumb or finger pressure on the actuating member and to continue broadcasting material from the devices. Therefore, in the absence of such a locking mechanism, once the finger or thumb pressure is removed all dispensing of material will cease whether such action is desired or not.
In other prior devices such as those known as the "Handi-Spred" Lawn and Garden Spreader of Precision Products, Inc. and "The Little Bit" Spreader of Global Products, Inc., the products are constructed to operate without maintaining pressure or force on the valve actuating and setting mechanism. In such devices, the extent of opening of the valve member to allow material to flow from the storage chamber to the broadcasting impeller is preselected by moving the actuating member into engagement with a locking mechanism which sets the valve opening at a preselected level. Thus, in order to shut off material flow with these devices, it is necessary to physically disengage the actuating member from the locking mechanism and move it to a position corresponding to a closed valve condition.
Thus, an inherent problem in the construction of these prior devices results from their tendency to continue dispensing material to the impeller even in the event that the impeller ceases to be rotated to broadcast such material. That is, since there is no automatic release feature in these so-called "on-off" or delivery devices, any momentary or extended cessation of operation of the device requires manual disengagement of the actuating member from the open or on condition to avoid undesired release of material.
Further problems have been encountered with these prior art devices in regard to the necessity to readjust the application rate to a specified level each time use of the device is resumed after some stoppage. Furthermore, these "on-off" devices have generally been found to be cumbersome in construction including more moving parts than automatic release, spring biased designs. Consequently, a problem of wear of the additional moving parts is presented by these devices.